Sound-box construction



y 1935- J. M, LUCARELLE 2,007,128

SOUND BOX CONSTRUCTION Filed Aug. 8, 1931 v v v I 2 //5 6 2 ATTORNEYS.

Patented July 2, 1935. I

J UNITED .sTAres PATENT OFFICE 5 Claims. (01. 274-27) I'his inventionrelates to sound-boxes and more particularly sound-boxes suchas areemployed for recordingsounds upon a; cylindrical wax recv rd blank.

One of the defects inherent in such soundboxes as have been heretoforeused for the re.

to sound'waves of relatively lowfrequency and weakly or inefficiently tosound waves of relatively high frequency. When a record made under theseconditions is reproduced, the sounds produced seem to be lower in tonethan the sounds recorded, and have lost many of their quality orpersonality characteristics. ,A well-known example of this defect is thereproduction of a wax cylinder record of the human voice. Through theloss of many of thehigher wave frequencies and apparent exaggeration ofthe sound waves of low frequency, the record when reproduced soundsunnatural and the voice is often. unrecognizable. Also the generalaudible effect is poor, and the reproductionunsatisfactory, often beingso dull and muffled as to be almostunintelligible. This is easilyunderstood when' it is remembered what a large part the high frequencyovertones have to play in determining the characteristic qualities ofthe voice. I i It is believed that the cause of the loss of the higherwave frequencies in recording is due to the fact that the energy ofspeech resides principally in the frequencies below 1000 cycles persecond and that articulationand intelligibility reside mostly in thehigher frequency sounds, those above 1000 cycles per second.Consequently the diaphragm of the sound-box, responding with greateramplitude to the low frequency sounds, produces a record in which thesesounds predominate.

Another objectionable feature of the usual type of sound-box is thetendency of the diaphragm to blast when a strong or loud voice'isrecorded. vThis seems to be due to the fact that the force of the loudvoice or musical note, as the case may be, is greater than theresponsive capacity of the diaphragm. A fluttering of the diaphragmresults which in a recorder produces breaks in What should be a smoothlycontinuous hill-anddale track formed upon the record-cylinder surface.When thereproducing stylus, in reproducing the record, travelsover thisportion thereof, it produces a harsh and foreign noise, in addition to adistorted reproduction of the original sound. Not only is the sound ornote more or less imperfectly reproducedbut the sound occasioned by theconcussion of the sapphire against the abrupt edges of the breaks in therecord track, is concurrent therewith.

ume and this may best be attained by the use of comparatively thindiaphragms, which, unfortunately, are more susceptible tobla-st thanthose of greater substance. V

; It is an object of the present invention to pro- 10 vide a sound-boxcapable of producing a record substantially free from the evils ofblasting, even when sound waves of relatively great amplitude areimpressed upon the diaphragm. Another object is to provide means adaptedto pre-' 15 vent blasting? even when diaphragms of exceptional thinnessare mounted in the sound-box.

Another object is to provide a device of the nature described capable ofrecording and reproduc-v ing in a highly natural manner. Another object20 is to increase the voice or tonal range of a sound- "The inventionaccordingly consists in the fea- 35 tures of construction, combinationsof elements,

and ai'rangementsof parts as will be exemplified in the structure to behereinafter described and the scope of the application of, which will beindicated in the following claims. I

In the accompanying drawing in which is shown one of the variouspossible embodiments of my invention: V r

Fig. 1 is a side elevation of a sound-box of a well-known type, showinga portion of the tonearm;

Fig. 2 is an end elevation'thereof;

Fig. 3 is a section taken on line 33 of Fig. 4;

Fig. 4 is a section taken on line 4'4 of Fig. 3, 50 and Fig. 5 is aperspective view of a leak-oif, damping and sound wave spreading device,employed .in my sound-box construction.

, Similar reference characters refer to similar 55 It is usuallydesirable to get considerable vol- :5

parts throughout the various views of the drawing.

The sound-box shown in the present embodiment of my invention involvesthe use of a sound wave bafile and leak-off. Referring to the drawing,the sound-box structure comprises a tonearm or tube I closed at its end,as by the wall 2 and which is provided with a downwardly turned flange 3surrounding a circular opening 4. The pan or sound-box head comprises ashallow inverted dishlike member 5 having circumferen tial walls 6. Thecircular edge 1 of an opening formed in the center of the pan is seatedin and secured to the tone-tube by turning the flange 3 over said edge,as at 8, as shown in my present construction, although it will beunderstood that the tone-arm and pan may be formed integrally. Such anintegral construction is shown in the patent to Bodine et al., No.1,606,744, to which reference is made for a description of the manner inwhich a combined recorder and reproducer may be mounted and anexplanation of its mode of operation as applied to a commercialdictating machine.

The pan is further supported by a boss 9 formed on the tone-arm l towhich the pan is attached by means of a screw ID. A diaphragm II issuitably mounted in the sound head, as by means of gaskets l2-|3, whichin the present construction are held in place by means of a fillet I4 ofplastic material such as beeswax. The diaphragm is preferably made ofmica, perforated at its center for the passage of a small screw l5,which is threaded into and makes fast to the diaphragm a stylus or pointholder l6. Holder I6 is further supported upon the diaphragm by means ofan arm I! having an offset portion l8, which, in assembling, is passedthrough a perforation in the diaphragm, as at I9. The stylus holder isof familiar form and provides a seat for a recording stylus 20 and areproducing stylus 2| either of which may be brought into operativeengagement with a record-cylinder, by means shown and described in theBodine patent referred to above.

No novelty is claimed for the features thus far described.

The upper wall of the tone-arm is perforated as at 22, by punching orotherwise, at a point directly opposite the center of the opening 4, toreceive a hollow funnel-like plug 23 terminating in an enlarged conicalend 24 which extends downwardly through the opening 4 into closeproximity to the diaphragm. The plug may be swaged tightly within theopening 22, or made fast therein in any other suitable manner. Theobject of this plug member is to prevent the impinging of sound wavesdirectly at the center of the diaphragm and to cause them to strike anannular portion of the diaphragm adjacent the periphery thereof, and hasother objects as will presently appear.

The result of this limitation of impact appears to be twofold. In thefirst place it serves to prevent blasting and thus ensures the tracingof a smoothly continuous track upon a record-cylinder during recording.This result permits the use of thinner diaphragms, from which it followsthat a tone of a certain intensity will produce sound wave tracks uponthe record of greater amplitude; and greater volume is attained when therecord is reproduced.

And secondly, it has been found that the deflection of the sound wavesaccomplished by the conical plug tones down the effect produced upon thediaphragm by vibrations of lower frequency and permits it to respondmore accurately to vibrations of higher frequency, thus enabling arecord to be made of these higher frequency waves and a consequentimprovement of the quality of the tone and the attainment of a higherpitch when the record is reproduced.

Many tests of the standard type of recorder-reproducer, in which theconical plug is omitted, establishes the fact that it is naturallyresponsive to sounds up to 2500 cycles per second and,

with increasing weakness, to sounds up to 4-300 cycles per second. Onthe other hand, tests with sound-boxes m which the conical plug was usedshowed that they were naturally responsive to sounds of 3500 cycles persecond and, with increasing weakness, to sounds up to 500% cycles persecond. As would be expected, this resulted in more natural recordingand reproducing, in that there were saved many overtones and othercharacteristics which determine timbre or voice personality. This resultis believed to be in part due to the damping effect of the air cushionestablished above the diaphragm and within the interior of thefunnel-shaped plug, which aids in preventing blasting and makes thediaphragm more responsive to sound waves of higher frequency.

But a further improvement in the action of the device when used as arecorder has been effected by the provision of a leak-off channel 26 inthe plug 23. This channel connects with the interior of the sound-box ata point just above the diaphragm through the conical end of the plug.The upper end of the channel is connected with the atmosphere exteriorlyof the sound-box by means of plural passages 28. A cap 29 fits snuglyover the upper end of plug 23 and has openings 30 in its cylindricalwall, which may be made to register wholly or to any desired partialextent with the openings 28. Although I have shown means for adjustingthe amount of leak-off, beneficial results. may be attained by the useof a leak-off of predetermined and invariable capacity, and under someconditions such an arrangement is preferable.

The chief benefit derived from the leak-oil seems to be that by its usethe recorder is able to handle with substantially equal efficiencyvibrations covering a wide range of intensity. The excess energy of aloud voice is drained off to the surrounding atmosphere so that thediaphragm is not put under an overstrain. This prevents rattle and blastof the diaphragm and ensures the production of a good record.

Waves of low frequency which have a larger share of the energy of speechthan those of high frequency, are leaked off to a greater extent thanare the latter, and thus the leak-off passage aids the baffling anddamping effects of the plug in effecting the recording of more of thehigher overtones or partials of the voice and so enhance the quality ofreproduction.

It will be seen that there is provided a construction of an essentiallypractical nature in which the several objects of this invention areattained.

As many possible embodiments may be made of the above invention withoutdeparting from the scope thereof, it is to be understood that all matterherein set forth or shown in the accompanying drawing is to beinterpreted as illustrative and not in a limiting sense. I

I claim as my invention: I

1. In a dictating machine, in combination. a

sound-box, a disk-shaped diaphragm in said sound-box supporting astylus, a sound-conduit connectingwith the interior of. said sound-boxthrough a circular opening which with respect to said diaphragm is ofrelatively small diameter, and a substantially funnel-shaped membermounted with its open base directed toward said diaphragm and its bodyextending through said opening into said sound-conduit, the diameter ofsaid member in the plane of said opening being substantially less thanthe diameter of said opening.

2. In a dictation recording machine, a soundbox, a diaphragm in saidsound-box, a tone-tube connecting with the interior of said sound-boxthrough a circular opening, a conical plug mounted in said opening withits base open and directed toward said diaphragm, and a leak-on passagein said plug connecting the interior of said soundbox with theatmosphere.

3. In a dictation recording and reproducing machine, a sound-box, adiaphragm in said soundbox supporting a recording and a reproducingstylus, a 'tone-tube connecting with the interior of said sound-boxthrough a circular opening, a hollow conical plug mounted in saidopening with its'base directed toward said diaphragm, and a leak-01fpassage in said plug connecting the interior of said sound-box with theatmosphere.

4. In a dictation recording and reproducing machine, a sound-box, adiaphragm in said soundbox supporting a recording and reproducingstylus, a tone-tube connecting with the interior of said sound-boxthrough a circular opening, a conical plug mounted in said opening withits base directed toward said diaphragm'a leak-ofi passage in said plugconnecting the interior of said sound-box with the atmosphere, and meansfor wholly or partially obstructing said passage.

5. In a dictating machine, in combination, a sound-box, a disk-shapeddiaphragm in said sound-box supporting a stylus, a sound-conduitconnecting with the interior of said sound-box through a circularopening which with respect to said diaphragm is of relatively smalldiameter, a substantially funnel-shaped member mounted with its openbase directed toward said diaphragm and its body extending through saidopening into said sound-conduit, and a leak-off passage'in said memberconnecting the interior of said sound-box with the atmosphere.

JOSEPH M. LUCARELLE,

